What is DOC and How Is It Treated?

Dissolved organic carbon (DOC) is a general description of the organic material dissolved in water.

Organic carbon occurs as the result of decomposition of plant or animal material, and a small part of the organic carbon may then dissolve into the water.

Organic material (including carbon) results from decomposition of plants or animals. Once this decomposed organic material contacts water it may partially dissolve.

DOC does not pose health risk itself but may become potentially harmful when in combination with other aspects of water. When water with high DOC is chlorinated, harmful byproducts called trihalomethanes may be produced. Trihalomethanes may have long-term effects on health. That is why DOC is a consideration when water is chlorinated.

Not only can Dissolved Organic Carbon promote the formation of trihalomethanes (THMs) in chlorinated water, it can also interfere with the effectiveness of disinfection processes such as chlorination, ultraviolet and ozonation. DOC can also promote the growth of microorganisms by providing a food source. In addition, it can add taste, odor and color.

Organic content is usually higher in surface water than in well water.

Removal of dissolved organic carbon is more commonly done by municipalities and water suppliers than by homeowners. City water suppliers have treatment strategies to draw on that aren’t available to residential users. They are also in a better position to prevent the formation of DOC, which is usually easier than treating it.

Treatment methods effective in removing DOC from water include: coagulation/flocculation processes, biological filtration, granulated activated charcoal and distillation. For residential water treatment, GAC is the most common and the most practical treatment. Distillers can be used for drinking water only.

Usually treatment is recommended if concentrations of DOC are greater than 5 mg/L. At that level, it is likely that chlorination will result in the formation of THMs in excess of EPA standards. Above 5 mg/L color of the finished water also becomes objectionable. For concentrations of less than 2 mg/L, color is usually not an issue and THM creation will be small.